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January 21, 2012

Four Little Stars

In the year 1610, Galileo Galilei was the first to document the moons of Jupiter. He saw 4 small stars beside the mighty planet. The next night he noticed they had moved. Even over the course of one night he could see them moving. Eventually, he realized that they were moons orbiting the planet as our moon orbits the earth. He was able, after much observation to predict where they would be at a given time with a great deal of precision.

At the time, this was truly groundbreaking stuff. Not only did he prove that there were things out there that could not be seen with the naked eye, he also dealt a huge blow to the geocentric, earth is at the center of everything model of the universe that had been around for thousands of years.

The ability to predict very precisely where the moons would be at a specific time was of great aid to the mapmakers and explorers of the day. They had already been able to determine the latitude they were at, but up until then, longitude was a problem, as they had no way of telling where they were. The moons of Jupiter provided them with a clock, and with that clock, a lot of fancy math and some carful observations, the could pinpoint their location on the earth with great accuracy.

Theses days, we know that in addition to Io, Europa, Ganymede and Callisto, the moons in this picture, there are at least another 60 or so smaller moons floating around Jupiter. These four are by far the biggest however.

Io is the innermost moon. It is the most volcanically active place in the solar system. There are hundreds of volcanoes, any number constantly in eruption. Europa is next out, the surface being ice. It seems like there is an ocean of liquid water underneath the cover of the ice. It is one of the places scientists are most hopeful of finding life. Ganymede is also ice, with the possibility of a little water layer, and Callisto is much like our moon, a solid chunk of frozen rock. All of them are around the same size as our moon.

This picture, taken through a telescope show three of the moons with Jupiter in the center. I had to overexpose the planet to make the moons show up.

Jupiter and its moons are probably my favorite thing to look at in the night sky.